effectual and fervent

The book of James is a wonder.  It is written by the half-brother of Jesus and is practical and noble at the same time.  The rich are taken to task in chapter 1 and chapter 5 (James 1:10, 5:1-6) and the prejudiced in chapter 2 (James 2:1).  He even addresses the high responsibility of teachers in chapter 3 (James 3:1)..  In chapter 5 he mixes the practical with the theological.  We find it in verse 13:

James 5:13        Is anyone among you suffering? He should pray. Is anyone cheerful? He should sing praises. 14 Is anyone among you sick? He should call for the elders of the church, and they are to pray over him, anointing him with oil in the name of the Lord. 15 The prayer of faith will save the sick person, and the Lord will raise him up; if he has committed sins, he will be forgiven. 16 Therefore, confess your sins to one another and pray for one another, so that you may be healed. The prayer of a righteous person is very powerful in its effect. 17 Elijah was a human being as we are, and he prayed earnestly that it would not rain, and for three years and six months it did not rain on the land. 18 Then he prayed again, and the sky gave rain and the land produced its fruit.
The KJV translates verse 16 as ""Effectual and fervent" prayer of the righteous.  

The translation conveys they truth nevertheless.  Christian Prayer is powerful in it's effect.  It produces results.   Praise God!